Air Masses

1. Air Masses What are they and why should we watch them? (Click on the image below to watch a short clip on air masses). As it moves, characteristics of an air mass 
change and so does the weather in the area 
over which the mass moves. Movement of Air Masses When air moves out of a region it formed over, it 
carries its temperature and moisture conditions with it. An air mass is an immense body of 
air that is characterized by similar 
temperatures and amounts of 
moisture at any given altitude.

2. Classifying Air Masses P (or polar) air masses form at high latitudes near 
the Earth's poles. Air mass that form at low latitudes 
are T (or tropical) air masses. The terms polar and 
tropical describe temperature characteristics over 
which they form. Polar air masses are cold while 
tropical air masses are warm. Polar & Tropical Air Masses The area over which and air mass gets its 
characteristic properties of temperature and 
moisture is called the source region. Air masses 
are named according to their source region. C (or Continental) air masses form over land. M 
(or maritime) air masses form over water. 
Continental and Maritime describe moisture 
characteristics of air masses. Continental air 
masses are likely to be dry while maritime are 
likely to be humid. Continental & Maritime Air Masses In addition to their overall temperature, 
air masses are classified according to the 
surface over which they form. There are four basic types of air masses. CP - continental polar which 
is dry and cool. CT- continental tropical which is dry and warm or hot. 
MP- maritime polar and MC-continental, with polar being colder, both 
being wet.

3. Weather in North America A majority of the weather in North America that is 
east of the Rocky Mountains, is influenced by cP and 
mT air masses. Continental Polar Air Masses Maritime Tropical Air Masses * Uniformly cold and dry in 
summer * Clear and old in the winter - 
cold front * No heavy precipitation * In Great Lakes can bring snow 
or showers (lake-effect snow) * warm, loaded with moisture * unstable * responsible for 2/3 of the 
moisture in N. America * Summer in central and east 
U.S. brings high temps. and 
oppressive humidity Maritime Polar Air Masses Continental Tropical Air Masses * have least influence on 
weather in N. Am. * hot dry masses in S.W. U.S. 
and Mexico affected * at western U.S. shore during 
winter brings low clouds & 
showers * inland it produces heavy rain 
or snow * in New England it brings cold 
snowy weather Only occasionally do these masses affect other 
regions other than the source.

4. Fronts When two air masses meet, they form a front, which 
is a boundary that separates two air masses of 
different properties. Fronts are often associated with precipitation. Types of Fronts: 1) Warm 2) Cold 3) Stationary 4) Occluded

5. Warm Fronts A warm front forms when warm air moves into an area formerly covered 
by cooler air. The front moves slowly and as a result in 
light-to-moderate precipitation over a 
large area for an extended period.

6. Cold Fronts A cold front forms when cold dense 
air moves into a region occupied by 
warmer air. Because the cold air lifts up the warm air 
it is often gusty winds and downpours.

7. Stationary Fronts A stationary front forms when two 
masses of air come together but 
neither of them displaces the other. Sometimes a stationary front is associated 
with gentle to moderate precipitation.

8. Occluded Fronts When a cold front overtakes a warm 
front, and occluded front forms. The characteristics are depending of the 
type of occluded front that forms.

9. Resources 1) Wikipedia.org 2) Google images 3) Youtube.com 4) Tarbuck & Lutgens. Georgia Earth Science. 
Pearson Education, 2009.